1. Field of Invention
The present invention relates to a power conversion device.
2. Description of the Related Art
A power conversion device is a device to convert electrical power and configured to convert any of AC and DC electrical power to the other or alter a frequency of electrical power by controlling switching operation of semiconductor elements included in the power conversion device such as Insulated Gate Bipolar Transistor (IGBT). There is a loss generated by switching on and off these semiconductor elements and having an electrical current flowing through these semiconductor elements. If a temperature of the semiconductor element becomes higher than a threshold operation temperature of the semiconductor device due to heat from the loss, the semiconductor device is not capable of stopping the current from flowing by its switching operation and the power conversion device could break in the worst case. Therefore it is necessary to appropriately cool the power conversion device while it is in operation.
There are plural semiconductor elements provided in a semiconductor module installed in the power conversion device. The power conversion device usually includes plural semiconductor modules which are connected in parallel with each other. It is desirable to keep temperatures of the semiconductor modules equal to each other when the temperatures of the semiconductor modules rise while the power conversion device is in operation. If there is a variation in the raised temperature between the semiconductor modules, a semiconductor module that is heated to a higher temperature than the others cannot be used longer than the others, which results in the power conversion device being less reliable.
As for cooling semiconductor modules included in the power conversion device, JP2011-120358A discloses “a power conversion device” comprising plural semiconductor modules each of which includes a switching device, a cooling device for cooling the plural semiconductor devices, and a condenser connected with the plural semiconductor devices, wherein one of the plural semiconductor modules that dissipates less heat than the others has the switching device either having a lowest gate resistance or base resistance, or having a lowest inductance on a current passage between the switching device and the condenser and a highest gate voltage or base voltage (See claim 1 of JP2011-120358A).